1. Field of the Invention (Technical Field)
This invention relates generally to raw material fire retardant constituents transported to a secondary manufacturing process in media, and more particularly to fire retarding surfacing media, including but not limited to fabrics, films and sheets, intended for consumption in the creation of fiber reinforced polymer (FRP) composites.
2. Description of Related Art
Note that the following discussion refers to a number of publications by authors and year of publication, and that due to recent publication dates certain publications are not to be considered as prior art vis-a-vis the present invention. Discussion of such publications herein is given for more complete background and is not to be construed as an admission that such publications are prior art for patentability determination purposes.
Typically, thermoset and thermoplastic resins are petroleum by-products that have generally undesirable burning characteristics, i.e., high flammability at relatively low temperatures, very toxic and acrid smoke, and rapid destructive flame spread. It is well known that the flammability of thermoset and thermoplastic resins can be reduced by incorporating flame retardant agents. However, when additives are used to fill these resins, a multitude of problems arise.
Synthetic polymer resins are frequently used in the manufacture of reinforced plastics, fiberglass laminates, and molded plastics. Composite polymer materials are widely used in such industrial applications as structural components, siding and roof panels, roof decking, cable trays and mechanical parts such as threaded rod and strut due to their corrosion resistance. Both thermoplastics and thermosetting plastics are also widely used by automobile, rail transportation and aircraft manufacturers because of their light weight and high strength.
The burning behavior of such materials, particularly those that are to be used in an enclosed environment, are of primary concern to the present invention. Many reinforced plastics can be designed to have a degree of fire resistance. Many fire retardant additives are available. Unfortunately, a large number of the prior art fire retardant compounds give off extremely toxic fumes, such as nitrous oxides, cyanide compounds, and a variety of toxic brominated compounds, such as hydrobromic acid (HBr), which causes pulmonary edema at relatively low concentrations.
Less toxic additives, such as aluminum trihydroxide (ATH), are inefficient and require loading levels that are so high that the desirable physical properties and characteristics of the finished product are dramatically diminished.
Those conventional polymeric additives have numerous problems associated with their use in a variety of ways. For example, during fabrication of a product, a thermoset polymer resin must have a sufficiently low viscosity to soak or “wet-out” the glass reinforcements prior to curing. This wet-out is necessary to achieve a high cross-link density within the finished product. However, when a fire retardant powder additive such as ATH is mixed into the resin in the necessary quantities for acceptable fire retardancy, e.g., perhaps as much as 60 parts in 100 parts of total mix, the resin viscosity increases dramatically as the styrenated resin wets-out the additive. As a result higher viscosity resin no longer has the ability to fully saturate the glass reinforcements.
To overcome this higher viscosity processing problem, virgin styrene is typically added to the mixed composition to lower the viscosity back to the required working viscosity range. Consequently, the resin contains a disproportionate, higher quantity of styrene. When the part has been processed and cured, the part contains a disproportionate quantity of cross-linked styrene and polystyrene. The heavily filled part has undesirable physical characteristics such as reduced tensile, flexural and shear strength. The only way to make up for the reduced physical strength characteristics is to produce a thicker, heavier, more expensive part.
Although the excessively high ATH fire retardant loading does reduce the likelihood of the part to combust, when exposed to an open flame or high radiant heat, the ATH inefficiently reduces combustion by liberating bound water. As the decomposition of the ATH complex continues, the additional styrene constituent makes a major contribution as a combustible fuel source, and provides the composite surface with a greater affinity towards flammability.
In addition, virgin and cured styrene is an egregious smoke generating compound, which significantly adds to overall smoke production of the part. Therefore, with ATH, there are processing problems which yield weaker parts, and which have the characteristic of generating larger quantities of toxic smoke.
To reduce the fire retardant loading in a thermoset resin, an alternative to ATH is a combination of decabromodiphenyl ether (DBPE) with antimony trioxide (ATO), e.g., less than 20 parts per 100 parts of total mix. However, an additional quantity of styrene is still necessary to reduce the buildup in viscosity.
When compared with ATH during a fire insult scenario, the brominated fire retardant package is more efficient at reducing flammability of the substrate than ATH. However, the brominated constituent package produces large quantities of dense, acrid smoke which is extremely toxic.
Bromine works as a fire retardant in a pyrolysing composite part by competing with oxygen in the ionization phase of the combustion reaction by generating large quantities of brominated acidic vapor, soot and acrid, thick particulate smoke. The formation of these compounds further reduces the availability of oxygen at the laminate surface, and the negative contributions due to the required styrene diluent are still present.
Although effective as a flame retardant, the smoke generated by brominated compounds renders the environment biologically toxic. A significant byproduct of the decomposition of decabromophenyl ether is hydrobromic acid (HBr). This acid is notorious for causing pulmonary edema when inhaled, having similar effects as mustard gas used in the First World War. In addition, many other brominated byproduct compounds are produced, which have significant toxicity, with the possible production of suspect carcinogens.
In the case of thermoplastics, the same issues arise with fire retardant additives. These plastics have the ability to be formed into various shapes and profiles with heat and pressure, without the presence of volatile organic compounds (VOCs) or hazardous air pollutants (HAPs). As an added benefit, thermoplastics may then be re-formed under heat and pressure to an entirely new shape and profile. This behavior makes them attractive for intermediary fabrication and re-cycling. Although fire retardant compounds are available that are easily processed into these polymers, the trade-off is they are almost exclusively brominated. These compounds are additionally attractive as they are the most economical. Nonetheless, upon combustion, they are the cause of the production of large volumes of smoke, rich with aggressive biological toxins.
The selection of a suitable smoke suppressant for curable and non-curable resins is not predictable. The selection is particularly difficult when flame retardants are employed, exacerbated by the complex interaction between the resin and the flame retardant agent. Although efficient in suppressing the rate of combustion of finished products that incorporate the resin, most flame retardants tend to affect adversely one or more key properties of the resin. For example, many flame retardant additives are ineffective at producing low density and low toxicity formulations.
It is well known that the flame retardant and smoke suppressive properties of additives in resin formulations vary greatly with the nature of the substrate. This is particularly true for intumescent compositions. The rapid formation of a protective char is highly dependent upon such factors as the combustion temperature, and the viscosity of the melt formed by the burning substrate.
Other considerations can also come into play, even where the properties of the retardant and suppressive properties of the composition are optimal. These considerations include the effect of the additive on the physical properties, color and molding characteristics of the base resin.
U.S. Pat. No. 3,293,327 describes the production of bicyclic phosphites, phosphonates, thiophosphates, and selenophosphates. These compositions are said to be stabilizers for vinyl halide resins. They are said to be useful as heat stabilizers for vinyl chloride resin, and as antioxidants for fats and oils.
Intumescent, fire-retardant coating compositions containing carbonifics, film-forming binders and phosphorous materials are well known in the art. U.S. Pat. Nos. 3,562,197; 3,513,114; 4,009,137; 4,166,743 and 4,247,435 disclose such compositions containing ammonium polyphosphates as the phosphorous containing material.
U.S. Pat. No. 3,654,190 discloses an intumescent paint comprising a resinous binder, a blowing agent, a phosphorous containing material, a source of chlorine a solvent, an anti-settling agent, a pigment and a surfactant.
U.S. Pat. No. 3,969,291 describes the use of an amide polyphosphate condensate as a fire-retardant additive in an intumescent coating composition. U.S. Pat. No. 3,914,193 discloses the similar use of a crystalline form of melamine pyrophosphate.
U.S. Pat. No. 4,166,743 describes an intumescent flame-retardant coating composition consisting substantially of a film-forming agent, an ammonium polyphosphate, one or more substances which are carbonizable under the action of heat, a dispersant, and optionally a filler. The coating composition additionally contains an ammonium polyphosphate activator weighing 0.5 to 50% of the weight of ammonium polyphosphate. The activator is constituted by at least one salt which contains water of crystallization which is liberated upon the composition being heated. As a coating, this material is unsuitable for fabrics.
U.S. Pat. No. 4,743,625 describes a flame-retardant polyurethane product that is produced by mixing and reacting a salt-forming compound with an acidic salt-forming compound containing phosphorus in a polyol and/or a polyisocyanate, and then reacting the polyol and polyisocyanate. That fire retardant mixture when exposed to excessive heat proceeds through two primary reaction phases. First, an early formation of a char layer is intended to slow the oxidative penetration into the foam core substrate, and second, a glassy layer of non-combustible vitrified material is intended to slow the penetration of radiant heat. However, borates and silicates typically melt together, at relatively low temperatures, to form brittle, fragile matrices. The fragile matrices there add no structural integrity to the char layer profile.
U.S. Pat. No. 4,801,625 describes a flame resistant composition having an organic polymeric substance in intimate contact with a bicyclic phosphorous compound, and a gas producing compound. The patent is silent on the use of bicyclic compounds to attain smoke suppressed flame retardant thermoset compositions.
U.S. Pat. No. 5,356,568 describes a solvent-based heat-resistant and fire-retardant coating containing carbonifics, film-forming binders, and phosphorous materials. Also described is an application where the coating is sprayed on steel and aluminum plates using a gravity flow gun. Not described are any smoke retardant properties, nor the use of the coating with resins or polymer plastics.
The development of additives for use with resins remains a highly empirical art. The predictability of the behavior of the final composition is rare to non-existent. The prior art has largely concentrated on developing highly specific additive combinations for particular resins and end-uses.
This is a particular problem when the fire retardant additive powder needs to be combined into composite structures and component products such as glass rovings, yarns, cloths, mat, and knitted fabrics. Typically, this is done by mixing the powder with high strength thermoset or thermoplastic resins. However, none of the prior art compounds are truly suitable for adding to curable resins.
The following U.S. patents describe flame retardants to be used with fabrics. However, those patents describe the fabric in a manner and style that is in contrast with the capabilities, functionality and specificity of the desired compounds and products. Exterior electrical cable wraps, door seals, a membrane to reinforce sprayable mastics or coatings or a mesh fabric with undefined intumescent materials are clearly in contradiction with the technical merits and uniqueness of the present invention.
U.S. Pat. No. 6,340,645 describes a flexible laminated fabric comprising a glass fiber web or glass fiber fabric coated with a four component intumescent composition. That composition is described as being suitable as a hot gas seal for fire doors, as fire protection curtains, and as fire protection windings surrounding individual cables or cable runs. The flexible fabric is intended for external use only to cover or seal a variety of components. The patent does not describe the ability of the intumescent constituent mix to reduce smoke when exposed to open flame. Neopentyl glycol and ethylene glycol phosphates have the propensity to generate smoke upon thermal decomposition. This is undesirable. That patent is extremely vague on the mechanism and smoke characteristics of the preferred polyol partial phosphates. The inorganic frame-forming candidate compounds are simple inorganic compounds which do not contribute significantly to structure.
U.S. Pat. No. 6,205,728 describes a laminated building component composed of a rigid resilient composite panel which is covered by a membrane. That membrane is selected from a group of non-combustible materials such as glass, quartz, carbon or stainless steel. The membrane is bonded to the panel with an adhesive and coated with a thin film fire protective intumescent coating. That membrane serves as a lath to hold and reinforce a spray, brushed or rolled intumescent coating. The patent is silent on the composition of the fire protective intumescent coating, and the coating's ability to reduce surface flammability or reduce smoke generated by the under-laminate structure.
U.S. Pat. No. 6,096,812 describes a low density epoxy-based intumescent fire resistive mastic coating with means for reinforcing the mastic with a carbon fiber mesh. That reinforced coating is strictly a surfacing treatment. Epoxies have a propensity to generate significant quantities of acrid smoke which can render an environment toxic. Additionally, the coating requires “at least one spumific” comprised of an isocyanurate. Isocyanurates are organic compounds containing nitrogen which can form hydrogen cyanide (HCN) as a thermal decomposition product contributing significantly to the toxic gas environment. That is also undesirable.
U.S. Pat. No. 6,001,437 describes a method for making high-temperature glass fiber by treating E-glass fiber with selected acids and then treating the fiber with organo-metallic material. Additionally, the patent describes the use of the fiber in thermal protective structures. The open weave mesh fabric is comprised of at least one layer of thermoplastic resin which had been pre-coated with subliming and/or intumescent material. The fabric may be pre-formed into a self supporting structure or embedded into a pre-existing structural automotive container.
Not described are specifics as to the constituents or processing ranges of the subliming or intumescent materials. No mention is made of a chemical mechanism which can reduce the flammability or smoke generation of the thermoplastic layer or underlying substrate.
In a combustion scenario, burning polypropylene thermoplastic produces particulate smoke, mostly carbon dioxide (CO2), some carbon monoxide (CO) and water (H20) Conversely, polyvinyl chloride thermoplastic, which does have an inherent fire retarding characteristic, combusts to form large quantities of hydrochloric acid (HCl) and acrid, chlorinated organic compounds. Hydrochloric acid vapor is extremely toxic for human tissue. A common result of exposure to hydrochloric acid rich smoke is impaired vision, respiratory pain and narcosis, resulting in confusion and possible loss of consciousness. All of these effects are undesirable. The patent is silent on the ability of the thermal protective layer to address the biologically toxic byproduct species created during combustion of the thermoplastic glass layer or the underlying thermoplastic substrate.
The physiological effects of exposure to heat in fires and/or the resultant toxic smoke can result in varying degrees of incapacitation, permanent injury or death. Visual obscuration and painful irritation of the eyes can impair or reduce the efficiency of egress due to psychological and/or physiological effects. Breathing difficulties, lung inflammation, narcosis and respiratory tract injury, are physiological hazards potentially present in fire scenarios. Narcotic gases, e.g., carbon monoxide, hydrogen cyanide and reduced oxygen, can affect the nervous and cardiovascular systems, causing confusion, a period of intoxication, followed by a collapse and loss of consciousness, followed ultimately by death from asphyxiation. Any prior art compounds that include materials that produce these effects are undesirable.
More particularly, even though they are effective fire retardants, for the reasons stated above, it is ideally desirable to provide a non-toxic finished product that does not include any of the following classes of compounds: Brominated compounds, including decabromodiphenyl ether (DBPE, Deca-BDE), octabromodiphenyl ether (Octa-BDE), pentabromophenyl ether (Penta-BDE), hexabromocyclododecane (HBCD), decadbromobiphenyl ether (DeBBE) as well as other polybrominated biphenyls (PBB), tetrabromo phthalic anhydride and all related aliphatic and aromatic brominated compounds.
Some polymeric manufacturing resins, e.g., polyester, vinyl ester, epoxy, and adhesives are available which have tetrabromobisphenol-A and/or derivatives of such brominated monomer flame retardant compounds incorporated into the backbone of the resin chain during the manufacturing process. These resins “carry” their bromine and do not require additives other than antimony trioxide (ATO).
The heavy metallic bromine synergist antimony trihydroxide (ATO) greatly assists bromine in fire suppression but is nonetheless a heavy metallic.
Therefore, it is desired to provide a disparate assembly, containing a disproportionately large quantity of fire retardant, that is capable of intimately combining with a rigid composite surface during a secondary manufacturing process. When the assembly is positioned to envelop a pre-processed schedule of raw fibrous reinforcement and polymeric resin, and the secondary manufactured product has reached completion, the resultant assembly has lower surface flammability than would otherwise be achieved by the substrate material alone.
Bromine compounds can be concentrated in a surface boundary layer of a composite that will provide a significant reduction in surface flammability characteristics. However, resultant combustion species will be abundant with biologically toxic compounds.
A more attractive embodiment would be a non-toxic fire retarded surface, such as the toxicity contribution that would be provided by aluminum trihydrate (ATH), however with the efficiency of brominated compounds.
Although any fire retardant constituent or composition is a candidate for inclusion into the transport media of the present invention, the preferred embodiment of the article of manufacture would not contain compounds that yield products with undesirable physical and flame retardant characteristics that are inconsistent with current building and life safety regulatory standards, and are physiologically toxic.